Rotary trench excavators are known to find a wide application for digging long distance trenches in a range of soils.
The use of single-bucket excavators in combination with drilling and blasting operations, or the use of ladder-type trenching machines is less productive and reliable.
There are known rotary trench excavators making use of crawler-type or sometimes wheel tractor pivotably connected to the working multi-bucket member. The working member can have a single rotor, or several kinematically or rigidly interconnected rotors.
For developing a sufficiently high pull force, especially for digging trenches of substantial cross-sections in very hard soils, the tractor, and eventually the entire trenching machine, must be very heavy. The overall weight of such an excavator is normally 50% greater than that of the proposed machine.
Expansion in the range of application of rotary trench excavators and their use for digging hard and permafrost soils, along with a growth in the length of pipelines and cross-section of trenches necessitate an increase in the pull force to be developed by the tractor or prime mover consequently resulting in a greater weight of the excavator and more power required for its movement.
Therefore, the use of single-rotor trench excavators is disadvantageous, or sometimes impossible.
More advantageous for use with high power prime movers is a construction of a trench digging member consisting of several independent rotors.
A construction which bears the closest resemblance to one to be herein described resides in rotary trench excavator (SU, A, 1,113,483) which comprises a semi-trailing working member including a movable frame with a wheeled support, and rotors mounted on a carrying frame. The carrying frame is disposed between the rotors and has cantilevers with ends thereof accommodated in the interior of the rotors. Soil is dug by this excavator at two sides of the pipeline resting on the ground, whereas part of the ground under the frame is removed by a passive mechanism, whereby it is impossible to dig a full-profile trench. In addition, with two rotating rotors the working member of the excavator fails to ensure digging in a direction coinciding with the movement of the machine or counter to the movement of the machine, since the first causes a vertical component of the digging force directed upwards, and the second causes a vertical component force directed downwards, both resulting in a moment acting in the lateral plane and therefore a higher dynamic range of the working member.
This technical solution makes it possible, in the case of using an independent drive for each rotor, to provide a working member wherein adjacent rotors rotate in the opposite directions only if one more active rotor of the same dimensions is installed therebetween, which necessitates displacement of such a rotor longitudinally to result in excessive length of the working member. Also, offsetting the rotors longitudinally calls for the provision of additional means for evacuating the soil being dug.